1. Field of the Invention
This invention relates, in general, to electrical motors and, more specifically, to electrical motor controllers.
2. State of the Art
Electrical motors are widely used in manufacturing operations to control machines, automated equipment, etc. Suitable controls or controllers are used with such motors to selectively control the direction of rotation of the motor and the duration or amount of rotation of the motor. In certain instances, such controllers selectively control the speed of the motor as well as its acceleration and deceleration between start and end positions.
Variable frequency motor drives have been coupled to induction motors to selectively control the speed of such motors by varying the frequency of A.C. electrical power supplied to the motor. Such variable frequency motor drives are wired to supply different frequency A.C. power to the motor in response to selected input conditions, such as the depression of an input switch, an input signal from an external control unit, etc. The variable frequencies are selected in advance during the design of the variable frequency motor drive, motor and driven member or machine.
However, such "hard wiring" dedicates the variable frequency drive to the motor so as to provide only a limited number of different A.C. power frequencies and the resultant available motor speeds. Thus, it would be desirable to provide an electrical motor position controller in which the speed of the motor can be easily controlled in a re-programmable fashion so as to enable the speed of the motor to be selected from a multitude of different speeds and changed, as desired, due to varying application requirements, manufacturing conditions, etc.
Electrical controllers, such as programmable logic controllers (PLC) are widely used in manufacturing operations due to their easy re-programmability. Such programmable controllers operate a stored control program which defines the application program controlling the operation of an attached machine. Reprogramming through an operator interface or programming panel is easily accomplished when it is desired to modify the operation of the machine or device controlled by the programmable logic controller. However, such programmable logic controllers have limited programming capabilities and have not been widely applied to electric motor controls.
Thus, it would be desirable to provide an electrical motor controller which enables the direction and degree of rotation of an electric motor output shaft to be easily selected and varied. It would also be desirable to provide an electrical motor position controller in which a plurality of selectible motor operating sequences may be selected. It would also be desirable to provide an electrical motor position controller in which an electric motor is driven through a sequence of operation which is comprised of a plurality of discrete steps, each containing a plurality of programmable features, such as destination point, event and/or speed. Finally, it would be desirable to provide an electrical motor position controller in which the speed of the motor may be easily selected from a plurality of different available speeds to meet application requirements.